There has been increased interest in the health effects of the Environmental Tobacco Smoke(ETS) as a confirmed human carcinogen. It has been known to be extremely difficult to make an accurate assessment of exposure to ETS since it is consisted of a variety of components and there are a number of labile chemicals. Therefore, it is necessary to obtain, to interpretate and to provide the data of quantitative exposure assessment to ETS in the field of environmental health. The purpose of this research is to evaluate the concentration of ETS using VOC in indoor office environments. The correlations and concentrations of benzene, RSP, 3-EP, nicotine that are indicators for ETS were investigate with smoking density, air change per hour(ventilation rate). Air samples were taken in smoking room(7 sites), smoking allowed office (3 sites), corridor outside smoking room(7 sites), non-smoking office (9 sites). The concentrations of benzene showed significant difference according to category of indoor office environments. The geometric mean concentration of benzene were 23.56 ${mu}{ extrm}{m}$/㎥(range 4.80~192.90 ${mu}{ extrm}{m}$/㎥) in smoking rooms. 6.16 ${mu}{ extrm}{m}$/㎥ in smoking allowed offices, 1.32 ${mu}{ extrm}{m}$/㎥ in the non-smoking offices respectively. The ratios of the concentration of benzene between outdoor air and smoking room, smoking allowed office, and non-smoking indicators concentrations, SD, and SI were 0.82(benzene and nicotine). 0.76(benzene and RSP), 0.60(benzene and SD), 0.76(benzene and SI). It is proposed that benzene is a good indicator for ETS.